A Japanese driver has captured the heart-stopping moment he was swept up by a tsunami as he drove along a coastal road.

The unnamed man was driving in Asahi City in the Chiba Prefecture last Friday when the ferocious wall of water struck.

The driver, who appeared to have a camera positioned on his car bonnet, described how the enormous wave surged over a road barrier and crashed down on the road in front of him.

"When I came to the fishing port and turned the corner I could see the wall of water," he said in an interview.

"At that moment I could do nothing else but keep driving. In the middle of that situation my car was taken by the wave."

The driver escaped unharmed but at least 11 others in Asahi have been confirmed dead, with roads destroyed and fishing boats, cars and homes swept up in the tsunami spawned by last Friday's 9.0-magnitude earthquake.

Across Japan the official death toll stands at 5692, but more than 9000 are still missing.

Australia's Department of Foreign Affairs and Trade has upgraded its travel advisory to Japan, telling Australians to leave Tokyo due to the radiation risk from the quake-hit Fukushima Nuclear Power Plant amid fears of a meltdown.

Foreign Minister Kevin Rudd has told Fairfax Radio the federal government will provide whatever practical assistance is necessary to Australians experiencing difficulties in getting out of the country.